An accurate description of jets and their structure poses numerous theoretical challenges. Despite the fact that
\(2 \rightarrow 2\)  processes involving either two jets or a jet and an electroweak gauge boson are known to next-to-next-to-leading
order (NNLO) accuracy in the strong coupling expansion, the presence of multiple scales, such as the jet transverse momentum, the
jet radius and the substructure variables we would like to consider, e.g. the jet mass, renders fixed-order
predictions in QCD insufficient. In order to achieve higher precision, fixed-order results need to be combined with
resummed calculations.
However, all-order evaluations of jet substructure observables are far from trivial due to the presence of hard
boundaries in phase space, which give rise to non-global effects [1]}, [2]}, and because of the algorithmic
nature of jet definitions that make all-order factorisations difficult to achieve. These challenges have been tackled by the
theory community over the past decade and nowadays, thanks to numerous QCD studies, e.g. [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}, [13]}, [14]}, [15]}, [16]}, a deeper understanding of jet substructure has been reached.
One of the lessons we have learnt from these investigations is that so-called grooming techniques, i.e. jet substructure algorithms that aim to clean up a jet by removing from its constituents the ones that originate from soft
physics, actually improve our ability to use perturbation theory to describe jet physics. They reduce the impact of
non-perturbative effects due to hadronisation and the underlying event (UE), for a recent review, see e.g. [17]}.
Furthermore, the all-order structure of the perturbative result is also simplified because groomers, such as the
modified-MassDrop/SoftDrop algorithm [3]}, [5]}, can eliminate the logarithmic enhancement due to soft gluons at wide angles,
including the intricate structure of non-global logarithms by turning logarithms of the observable under consideration into logarithms of an external parameter, such as \(z_{\text{cut}}\)  in the case of SoftDrop .
